The present invention relates to a method of and an apparatus for controlling display of screen data communicated between a host computer and a terminal equipment called a video data terminal, and in particular, to a method of and an apparatus for controlling communications of screen data by use of a communication line such as a packet network.
In the prior art, according to the method of controlling a screen display of the most common terminal equipment (to be simply referred to as a terminal herebelow), screen data is received from a host computer (to be simply referred to as a host herebelow) so as to display the screen data on a display of the terminal and then data to select the next screen is inputted and is transmitted to the host, which as a result causes the host screen data for the next display to be received from the host, thereby displaying the screen data.
As another conventional example of the screen display control method, there has been known a method in which there is beforehand disposed on the side of a terminal equipment a file containing fixed screen data. That is, the primary screen of the host is subjected to a download or is loaded such that when the host sends only the data associated with a screen number is sent to the terminal, the corresponding fixed screen data is read from the file on the terminal side so as to be displayed on a display. In addition, when additional screen data is necessary for the fixed screen data, the additional screen data is generated in the host and is then sent to the terminal. For details, refer to the JP-A-60-156138, for example.
However, in the former method, although the constitution of the terminal can be simplified, the screen data is transmitted from the host to the terminal each time the screen data is changed, which leads to a problem that the amount of data transmitted via the communication line becomes great and that the frequency of line utilization as well as the period of time of line occupancy are increased and hence the utilization efficiency of the communication line is decreased. In addition, there exists a problem that a long period of time is required for a switching operation between displayed screens.
On the other hand, according to the latter method, since the file containing the fixed screen data is disposed on the terminal side, the transmission of the fixed screen data is unnecessitated and the amount of data to be transmitted between the terminal and the host is considerably minimized; however, in a case where the screen data is systematic data such as those configured in a tree structure, each time the present screen is switched to the subsequent screen, it is required to receive a screen number (ID) data and additional screen data from the host, which leads to a problem that a long display switch time is necessary and that the number of data transmissions to the host is kept unchanged as compared with the former method.